(1) Field of the Invention
The present invention relates to a planar magnetron sputtering apparatus which forms a thin film by the use of sputtering. More particularly, it relates to a sputtering apparatus of good step coverage by which a substrate to be formed with a film and having a microscopic via-hole or the like as the shape of a stepped part can be formed with the thin film conforming to the shape.
(2) Description of the Prior Art
A conventional planar magnetron sputtering process is described in detail in, for example, a paper by JHON L. VOSSEN, WERNER KERN et al. contained in "Thin Film Processes", ACADEMIC PRESS, 1978.
A material to be sputtered is sputtered and scattered by an inert atomic species heavier than a hydrogen atom, such as Ar, thereby to reach a substrate on which a film is to be formed. The directions of the scattering are controlled according to the cosine law. Therefore, when a stepped part exits on the substrate to be formed with the film, overhangs are formed on the side walls of the step.
The actual film formation by the sputtering is employed for the production of semiconductor devices (ICs, LSIs, etc.) and various thin-film modules (thermal printing heads, etc.). More concretely, it is important as a technique for forming an interconnection layer, a conductor layer and an insulator layer.
As described in, for example, a paper "Vacuum Evaporation and Sputtering Apparatus" by Kitabayashi et al. in `Denshi Zairyo (Electronics Material)`, 1981, Separate Volume, pp. 143-148, there has been developed an apparatus in which a plasma is confined into the vicinity of a target by an electromagnetic field, thereby to efficiently form a film.
Besides, in a paper "Planar Magnetron Sputtering Cathode with Deposition rate Distribution Controllability" by Abe et al. in `Thin Solid Films`, Vol. 96 (1982), pp. 225-233, a double magnetic pole type electromagnet cathode structure is introduced. Here, it is claimed that a semiconductor substrate of large diameter (.phi.150 mm) can be formed with a uniform film by operating two electromagnets to control an electromagnetic field distribution and to change an erosion diameter at will.
Even with the techniques as mentioned above, however, the microminiaturization of patterns has been attended with the problem that, in a via-hole portion or the like in the case of forming the upper layer of a multilayer interconnection or an object to be formed with a film, already having an interconnection as an under layer, the step coverage becomes insufficient to cause a part where no film is formed.